Best Buy uses an automated process that many other retailers use such as Amazon. It tracks the returns you do related to the actual purchases. Certain kinds of returns flag higher such as high dollar value or buying and returning the same product more then once. IE someone buying HDTVs and then returning them a few times.
Based on your description you are probably pretty close to the line if you don't also buy a good number of items and keep them. I say this as an Elite Plus member who has myself already spend $12k at Best buy this year and who last year almost hit $40k. I have never once triggered the return blacklist but I buy such a large number of high value items from them that I would be very surprised if I did. I did ask a few of them how that process worked a couple times out of curiosity. Unfortunately I will be returning my Samsung Galaxy S 8.4 today though as the battery life and CPU just can't be justified for me over my iPad Mini Retina with Cellular Data for my needs. I really wanted them to though with that screen.
In just this month I have bought from Best Buy
Samsung Galaxy Tab 4 8.0
Samsung Galaxy Tab Pro 8.4 (quantity 3) for my 2 sons and wife
Samsung Galaxy Tab S 8.4 for myself as a trial to replace my iPad Mini Retina
Microsoft Surface Pro 3 To replace my Lenovo Yoga Pro 2
Microsoft Surface 2 for my father in law
Nokia 521 Phone for my older son